Electric machines, such as electric motors and/or electric generators, are used in in energy conversion. In the aircraft industry, it is common to find combination of motor and generator mode, where the electric machine in motor mode is used to start the engine, and, depending on the mode, functions as a generator, too. Regardless of the mode, the machines typically include a rotor having main windings that are driven to rotate by a source of rotation, such as a mechanical or electrical machine, which for some aircraft may be a gas turbine engine.